The invention relates generally to solar air heaters. Most solar air heaters work on the same principle as a greenhouse wherein sunlight is converted to heat within a glass or plastic covered enclosure. The heat is then trapped in the enclosure by the glass or plastic. Solar heating is an economical way for persons to augment the heating of homes and other buildings. The devices can be economical to build or buy and energy from the sun is free. Still, prior art devices are not as efficient as homeowners or other building owners would like. The reason for this, at least in part, is because cold incoming air is allowed to mix with the heated air in the solar air heater. Such mixing decreases the average temperature of the air in the heater and, thus, reduces the overall efficiency of the heater.
Prior art solar air heaters have tried to increase efficiency by one or more of, for example, increasing the size of the heater, increasing the surface area for radiant energy absorbance within the heater without increasing external surface area or increasing the layers of clear, transparent or translucent material covering the device. One prior art solar air heater is described in the book “Solar Air Heater” (Ray Wolf, Rodale Plans, 1981). This solar air heater tries to increase efficiency by increasing the surface area of the heater. This heater is described as a 4 foot by 8 foot enclosed space covered with translucent fiberglass cloth where cold room air is forced into the device at the base, heated by solar energy and then expelled from outlets at the top back into the room. The enclosure is one large area where cold air can mix with warmer air thereby bringing down the average temperature of the air within the device and, thus, lessening the temperature of the air being expelled back into the room. Additionally, the device is designed to permanently mount on an external wall of the building. Many homes may not have such an expanse of wall space conveniently located for both best sun exposure and best room air exchange.
Another example of a prior art solar air heater is described in U.S. Pat. No. 4,034,736 to Telkes. This design uses a plurality of parallel, horizontally disposed slats resembling a venetian blind thereby increasing the surface area where sunlight may strike and warm the air. Still, this device has the problem of a reduced average temperature since it also permits the mixing of incoming cold air with the warm air in the device.
Other heaters trying to achieve the goal of increasing the surface area of where sunlight may strike have been described. One heater uses highly polished aluminum fins to increase the surface area of solar energy absorbing material without increasing the overall dimensions of the device (see, Bevil and Brandt, Solar Energy, 12:19-29, 1968).
In another prior art device, McCullough (U.S. Pat. No. 4,262,657) increases the efficiency of a solar air heater by utilizing a clear glass or plastic honeycomb-style structure either directly behind the front panel or directly on top of the collector plate (i.e., the back panel) to block reradiation loss and by utilizing a vertical porous solar energy absorbing material through which the air passes to be heated. This design of McCullough, although an improvement over other prior art designs, only minimizes the mixing of cold incoming air with heated air. This is because the vertical porous panel of McCullough extends over the entire area of the heater. Since the system is not designed to ensure positive pressure evenly over the entire surface of the vertical porous panel nor reduce or eliminate airflow eddies, the system permits the back flow of air through the vertical porous panel resulting in loss of efficiency by the heater.
Still other prior art solar air heaters have tried to increase efficiency through tighter construction, insulating the device and increasing the number of transparent or translucent covers. However, all of the prior art solar air heaters known by the Inventor fail to address the problem of cold incoming air mixing with heated air.
What is needed is a solar air heater with increased efficiency over prior art solar air heaters.